Electrical cables are used extensively in oil wells to transmit electricity from above ground power units to pumps located many feet below the earth's surface. These cables must be able to survive and perform satisfactorily under extremely adverse conditions of heat, mechanical stress and pressure. In particular, these cables experience down-hole pressures which can be in the hundreds or thousands of pounds per square inch. Typically, the insulation surrounding the conductors in the cable contains micropores into which gas is forced at these high pressures over a period of time. Then, when the cable is rather quickly extracted from the well, or when the fluid level in the well is rapidly reduced, there is not sufficient time for the intrapore pressure to bleed off. As a result, the insulation on the cable tends to expand like a balloon and may rupture.
Presently, most high temperature and pressure oil well round cables are made by taking three stranded elements of conducting material, filling each of the strands with a blocking agent to prevent gas migration along each strand, insulating each strand with an appropriate insulation material, surrounding the insulation with a tape, sold under the registered trademark Tedlar, placing a braid of treated nylon over the Tedlar tape, cabling the three conductors about a central filler cord made of insulated string, surrounding the three conducting assemblies with a filler material and then armoring the entire cable assembly.
However, while there has been much work in this area of protecting down-hole insulated electrical cables to avoid explosive decompression by adding reinforcing layers, there are numerous disadvantages to this prior art. These disadvantages include the fact that many of the prior art cables are extremely expensive to manufacture, are bulky, will still rupture under adverse conditions and include numerous extra layers of protective material.
Examples of such cables are disclosed in the following U.S. Pat. Nos. 2,690,984 to Crandall et al.; 2,930,837 to Thompson; 3,299,202 to Brown; 3,425,865 to Shelton, Jr.; 3,602,632 to Ollis; 3,602,636 to Evans; 3,649,744 to Coleman; 3,684,644 to Snell; 3,742,363 to Carle; 3,835,929 to Shuman, Jr.; 4,096,351 to Wargin et al.; 4,106,961 to Kreuger et al. and 4,409,431 to Neuroth, and Japanese Pat. No. 22,677 to Fujikura.
In addition, cables have been developed in which the filler material is placed between or around the conducting assemblies in the unvulcanized state and is in turn surrounded by a metallic or non-metallic sheath or outer covering without undergoing vulcanization. The entire cable structure is then heated until the filler material vulcanizes, thus bonding either partially or completely, the filler material to the outer covering. Examples of these cables are disclosed in the following U.S. Pat. Nos.: 2,544,233 to Kennedy; 2,727,087 to Hull; 3,236,939 to Blewis et al; 3,413,408 to Robinson; and 3,462,544 to King.
However, these cables still possess the disadvantages of the first group of cables enumerated above, including that the cables may still rupture under adverse conditions, are relatively expensive to manufacture and are unnecessarily bulky.
Therefore, it is apparent from the above that there exists a need in the art for an electrical cable which is inexpensive, less bulky, more resistant to rupture and yet transmits electricity effectively. This invention addresses this need, as well as other needs which will become apparent to those skilled in the art, once given this disclosure.